An apparatus for heating breathing gas for divers, comprising an electric heating source which is arranged to transfer heat to breathing gas in a gas line in a diving equipment supported by divers, is previously known from U.S. Pat. No. 3,107,669. Such a known heating apparatus is intended directly or indirectly to supply the diver with heat energy in the purpose of reducing the diver's heat losses, especially at jobs in cold waters. Normally the diver wears a heat insulating diving dress which reduces heat losses to the surrounding cold water. The diver is cooled down or chilled partly by heat losses via the diving dress to the ambient cold water, partly by losing body heat via the lungs to the cold breathing gas. By heating the breathing gas, primarily heat losses to the breathing gas are reduced, and at further increase of the breathing gas temperature heat can be supplied to the diver's body via the lungs and the blood system, and this heat will partly compensate for the heat loss from the body to the ambient water. The requirement of supplied heat energy varies depending on how well the dress isolates, and how large the diver's own heat production is due to the word performed.
The apparatus revealed in U.S. Pat. No. 3,107,669, however, has not proved to be suitable for practical use. At diving jobs, especially at relatively large depths, a breathing gas is often utilized, the composition of which deviates from the composition of atmospheric air, for example thereby that the nitrogen largely has been substituted by noble gases, and thereby that the oxygen content is increased. Furthermore, it is required that the heating apparatus be able to supply relatively high heat flow to the breathing gas, and in this connection a heating effect of for example 200 W may be suitable. The U.S. patent teaches that an electrically heat wire shall be fitted exposed to the gas in the mouthpiece of the equipment, which is also provided with inlet and outlet valves for the gas. If the heating wire or element should have such a surface area that the required heat effect could be transferred to the breathing gas flow without any risk for momentary unpermissible super heatings of the breathing gas, the surface area volume requirement and weight of the heating element would be relatively large, which in turn means that the mouthpiece would be uncomfortable to carry, and furthermore, the mouthpiece would hamper the field of sight, and, therefore, such a mouthpiece would not be useful at demanding tasks. Moreover, the heating element is located close to the diver's face, and it is appreciated that an electrical malfunction in the heating element easily could bring about that electricity is conducted to the diver as the breathing out gas is moist.
Moreover, there are boiling systems known for transforming liquid oxygen into gaseous state whereby to put the oxygen in a form suitable for breathing purposes. At such apparatus (vide for example U.S. Pat. No. 2,515,835) simple heat exchangers are utilized, and the known systems of this sort do not provide any technique useful in connection with diving works performed in cold water.